"Biological Raw Materials" generally refer to so-called regenerative raw materials, i.e. raw materials which are biologically recoverable with a production rate that approximately corresponds with the consumption rate as opposed to fossil raw materials where the formation of which takes considerably more time than their consumption.
A biological raw material may, for instance, be supplied as a fine powder with a substantially still undamaged cell structure or with disintegrated structure. Biological raw materials can also be obtained as so-called biological organic waste. Biological raw materials substantially contain the elements carbon, hydrogen, oxygen and nitrogen.
Directly converting hydrogen into electric energy by means of fuel cells is well known. As compared with thermal heat engines, fuel cells offer the advantage of not being subjected to the principal thermodynamic restrictions of the efficiency resulting from the Carnot cycle. Fuel cells are theoretically able to convert combustion heat from the reaction of hydrogen with oxygen to water practically completely into electric energy. Therefore, clearly higher efficiency values can be obtained in practice with fuel cells than with thermal heat engines without any particular difficulties. This, however, takes for granted that the catalysts of fuel cells will not be poisoned by catalytic poison which may be contained in the hydrogen gas fed to the fuel cell.
Molecular hydrogen as a raw material is not naturally available but must be extracted from hydrogenous raw materials. Generating hydrogen from water by means of normal electrolysis consumes more current than can be generated with hydrogen, and is for that reason, of course, out of the question. The catalytic separation of water into hydrogen and oxygen is very slow and yields only small quantities with high expenditure of energy, thus offering no advantage for commercial utilization.
Generating so-called synthesis gas which substantially contains hydrogen and carbon monoxide, from coal and the installations required for this generation have been well known for a long time. This process is called coal gasification. The carbon monoxide in the synthesis gas can be converted into hydrogen and carbon dioxide by adding steam at elevated temperatures in a so-called water shift reaction.
Using synthesis gas to operate fuel cells is basically possible, but considerable disadvantages have been obvious in practice. Firstly, coal usually contains sulfur of natural origin which is entrained in the synthesis gas as gaseous sulfur compounds. Sulfer compounds are as a rule high-grade catalytic poisons which may irreversibly deactivate the catalyst of a fuel cell and, thus, the fuel cell itself. Sulfur-containing gases are undesirable emissions as environmental hazards. Secondly, generating synthesis gas from coal is expensive because of the accumulated costs resulting from underground mining, coal gasification and the necessary desulfurization.